The present invention relates to final drive and differential units for motor vehicles, and more particularly, but not exclusively, to a lublication mechanism in the final drive and differential unit.
Final drive and differential units are known of the type which comprises a differential carrier integrally formed with a cylindrical support structure and arranged to store an amount of lubricating oil therein, a differential gear unit rotatably mounted within the carrier, a ring gear contained within the carrier and mounted on the differential gear unit for rotation therewith, and a drive pinion shaft supported by a pair of axially spaced bearings mounted within the cylindrical support structure, and in which the drive pinion shaft extends outwardly through an annular oil seal member mounted within an outer end portion of the support structure and is integrally provided at its inner end with a drive pinion in mesh with the ring gear.
In such a final drive and differential unit as described above, the bearing facing the interior of the carrier is directly splashed with lubricating oil picked up by rotation of the ring gear, but the other bearing and the oil seal member may not be splashed with the picked up lubricating oil. It is, therefore, necessary to provide positive lubrication of the latter bearing and the oil seal member so as to ensure durability of the final drive and differential unit. In this respect, there has been proposed a lubrication mechanism for the bearing and the oil seal member, wherein an oil supply passage is formed in the upper portion of the cylindrical support structure to receive the lubricating oil picked up by rotation of the ring gear and supply it into an annular space around the drive pinion shaft between the bearings, and an oil return passage is formed in the bottom portion of the cylindrical support structure to permit the lubricating oil passing through the other bearing to return into the interior of the differential carrier. In such arrangement of the oil passages in the cylindrical support structure, it is difficult to effect sufficient lubrication of the bearing and the oil seal member during low speed rotation of the ring gear. If the oil supply passage is arranged to supply a sufficient amount of lubricating oil during low speed rotation of the ring gear, the oil seal member will be supplied with an excessive amount of lubricating oil during high speed rotation of the ring gear, resulting in leakage of the oil across the oil seal member.